Gaskets have been known that exert sealing properties by being held between opposite flange joint surfaces with a bolt. Such gaskets include a sealing portion formed in a shape of the flange joint surfaces. The sealing portion adheres between the opposite two surfaces without clearance by tightening with a bolt, and thereby the airtightness is improved.
Nowadays downsizing and a weight reduction are promoted for electrical parts and electronic apparatuses of a vehicle. As a result, structural materials for the electrical parts and electronic apparatuses have lower stiffness, the diameter and extension capacity of a bolt are reduced, and the number of parts tightened with a bolt tends to be decreased. A compressive load of a gasket thus tends to be smaller. In addition, the distance between bolts tends to be increased because of an enlargement of a case resulting from a variety of electrical parts provided therein and because of a reduction of the number of parts tightened with a bolt.
As a sealing configuration and sealing method used under circumstances with a reduction of a tightening load, inferior properties on a flange surface due to lower stiffness, and the like, such methods have been applied that join opposite flange surfaces by applying liquid packing between the joint surfaces and that tighten flanges with a rubber-like elastic body put in a groove fabricated on either of the flanges.
However, the conventional scaling configurations and sealing methods have a problem in that productivity is decreased in such a ease that parts are reassembled for reproduction. They have another problem in that handling for maintenance in the aftermarket is difficult. As a solution for these problems, a metal gasket forming a rubber-like elastic layer made of materials such as NBR and foaming NBR on either of or both of thin metal plates is taken notice because of its excellent form stability.
This kind of metal gasket, however, has a problem in that sealing properties are decreased because the thickness of the rubber-like elastic layer widely changes under the joint conditions of low stiffness in a flange and a reduced tightening load. In addition to the low stillness in a flange, an extension of the distance between bolts results in an increase of the flexure of a flange, which is another factor for decreasing the sealing properties. There is another problem that because the metal gasket is manufactured by progressive press working of a coil material, portions except a sealing portion are discarded as cut-out scraps when the size of a case is increased. That renders the yield rate of a material smaller compared with liquid packing and a rubber-like elastic body.
As a gasket that prevents the looseness of a bolt and improves the airtightness of an apparatus, a gasket is known that provides a circular metal frame and a sealing portion in an elastic body circularly extending toward the internal circumference portion of the metal frame and connected to the metal frame. The metal frame forms a through-hole where the shank of a tightening material that tightens between the two surfaces penetrates, and has a bearing corresponding portion that corresponds to the bearing of the tightening material around the through-hole (JP-A-2010-121715).